This disclosure relates to nanotubes and nanorods having piezoelectric properties and to devices manufactured therefrom. More specifically, this disclosure relates to nanotubes and nanorods that comprise polyvinylidene fluoride that can be used in actuators or sensors.
Piezoelectricity or pyroelectricity is the ability of some materials to generate an electrical potential in response to applied mechanical or thermal stimuli, respectively. The piezoelectric effect is reversible in that materials that exhibit the direct piezoelectric effect (the production of electricity when stress is applied) also exhibit the converse piezoelectric effect (the production of stress and/or strain when an electric field is applied). As a result of these advantageous properties, piezoelectric materials are used in a variety of applications such as for example, the production and detection of sound, the generation of high voltages, electronic frequency generation, microbalances and the ultrafine focusing of optical assemblies.
The piezoelectric effect is demonstrated by a variety of naturally occurring materials as well as man made materials. Examples of naturally occurring piezoelectric materials are quartz, Rochelle salt, cane sugar, topaz, bone, and the like, while examples of man made piezoelectric materials are barium titanate, gallium orthophosphate, lead titanate, lead zirconate titanate, potassium niobate, lithium niobate, lithium tantalate, polyvinylidene fluoride, and the like.
Polyvinylidene fluoride is a polymeric material that exhibits piezoelectricity in an amount that is several times greater than that exhibited by quartz. As a result polyvinylidene fluoride films are often mentioned as candidates for potential commercial applications in electromechanical and thermomechanical transducers, acoustic, infrared and temperature sensors, vibration, impact and stress/strain sensors, micro-actuators and switches, ultrasonic devices, power generators, microphones and hydrophones.
Polyvinylidene fluoride and its copolymers are a primary means of achieving mechanical and thermal sensitivities owing to its piezoelectric and pyroelectric properties. However, these properties have only been realized as bulk films. The bulk films unfortunately display low resolution sensing. Bulk films of polyvinylidene fluoride possess excellent piezoelectric and pyroelectric coefficients (32×10−12 coulombs per newton and 4×10−9 coulombs per square centimeter-Kelvin, respectively), which interface well with commercially available instrumentation. In theory, a bench-top electrometer capable of detecting 10 femtocoulombs to 20 microcoulombs interfaced with 1 square centimeter bulk polyvinylidene fluoride film, should be capable of detecting a pressure as low as 3 Pascals or a temperature shift of 2.5 microKelvin. However, in reality it is difficult to produce bulk polyvinylidene fluoride films that can display the aforementioned characteristics. Problems associated with the processing (e.g., melt-processing and solution casting) of bulk polyvinylidene fluoride based materials limit the size of the films produced. As a result, these materials cannot successfully be interfaced with nano- and micro-electro-mechanical systems thereby limiting their capabilities. The application of bulk polyvinylidene fluoride based materials to high resolution two-dimensional piezoelectric sensors, actuators, and the like, therefore continues to remain a challenge.
It is therefore desirable to develop piezoelectric polymeric structures that can be used for applications that involve sensors, actuators, and the like, and that can interface with devices that have nanometer sized and micron sized dimensions.